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[timotheos]

I tried to set up a cistern that would refill itself as I used it up without me having to keep an eye on it. It seems I messed up and now my hospital and workshops are underwater. and I can't get to the emergency cut off lever.
I had a pressure plate set to water level 3 on the bottom level another to water level 5 on the z level above both linked to a flood gate by the river 5 levels higher. I thought this would keep the water between those 2 limits.
What piece of dwarven idiocy did I miss? and how do i fix it for next time?

[proxn_punkd]

Triggering the pressure plates tells them to open a connected floodgate, not to shut it. So when your 5-deep pressure plate was triggered, it sent a signal to open the floodgate that the 3-deep pressure plate had already opened.

[Sphalerite]

Pressure plates don't send toggle commands, they send an 'open' command when their conditions are met, and a 'close' command when their conditions are not met.  If you set a pressure plate to activate when the water is above 5/7, it will send an 'open' command when the water goes from 4/7 to 5/7 (or above), and a 'close' command when the water goes from 5/7 to 4/7 (or below).  These are one-time commands, that aren't sent constantly when the conditions are met, so the floodgate will essentially follow the most recent command it gets.

The way to do what you're trying to do is with a single floodgate, set to trigger when the water is say 5/7 or below.  It will open when the water is less than that, and close when it is higher.  I've found this to not be terribly reliably however.  It's much safer to use a pressure break through a diagonal passage and then just let the cistern fill by gravity with no pressure plate required.

[timotheos]

Ok that's confusing because the first (3/7) plate on the lower level did close the flood gate as the water went from 0/7 past 3/7 and I had to re open the gate with the lever. The higher level 5/7 plate then also shut the flood gate when its level was reached.

[Garath]

always put your emergency lever somwhere where the water cant get to unless in a nighmare, not anywhere near the instalation. I think you can set notes, which are supposed to be used militairy, but are great for noting which lever toggles what

[eggrock]

The Repeater is an easy way to autofill a cistern and trigger your spike rooms. I wouldn't use the exact design on the wiki but it's a good concept (bridge vs. floodgate triggers.)

[Triaxx2]

Why not fill with a pump from a lower level? That'll keep the water from flowing higher than the pump? Plus done right, the pump will power itself.

[Sutremaine]

How about doors? They open and close immediately, so water shifting back and forth over the pressure plate and toggling it constantly won't spam the door with commands it can't carry out until it's done executing the last one.

Depressurising the water at the appropriate level is probably the safest option. Alternatively, you could have a pressure plate on the level above the reservoir set to close the floodgate if it detects any water at all.

[Quietust]

Pressure plates don't send toggle commands, they send an 'open' command when their conditions are met, and a 'close' command when their conditions are not met.

An important distinction (which you probably intended to include but simply forgot): they send their close command after their conditions have not been met for 100 ticks (the same delay between pulling a lever and a floodgate/bridge/whatever responding).

[DVeL]

How about doors? They open and close immediately, so water shifting back and forth over the pressure plate and toggling it constantly won't spam the door with commands it can't carry out until it's done executing the last one.

Depressurising the water at the appropriate level is probably the safest option. Alternatively, you could have a pressure plate on the level above the reservoir set to close the floodgate if it detects any water at all.

And how can i set pressure plate to CLOSE floodgate? My own attempts never succeeded.

[NecroRebel]

And how can i set pressure plate to CLOSE floodgate? My own attempts never succeeded.

You use a device called an inverter. Basically, these devices involve a pressure plate linked to powered disengaged gear assembly that is, in turn, linked to a screw pump. In the screw pump's input tile is a pressure plate that triggers on 7/7 water that is linked to the floodgates you want to close when the first pressure plate is triggered and 7/7-depth water. When the first pressure plate is triggered, it engages the gear assembly, thus powering the screw pump and pulling the water off the second pressure plate, thus causing it to turn off and send a "close" signal to the floodgates.

Alternatively, you use single-tile drawbridges, which always raise (forming impassible tiles) when floodgates open and lower (forming passable tiles) when floodgates close. Much simpler.

[Sphalerite]

How about doors? They open and close immediately, so water shifting back and forth over the pressure plate and toggling it constantly won't spam the door with commands it can't carry out until it's done executing the last one.

Depressurising the water at the appropriate level is probably the safest option. Alternatively, you could have a pressure plate on the level above the reservoir set to close the floodgate if it detects any water at all.

And how can i set pressure plate to CLOSE floodgate? My own attempts never succeeded.

Set the pressure plate to trigger when there is no water (level 0-0 or 0-1).  Link it to the floodgate.  Also build a lever and link it to the floodgate.  Pull the lever, this will open the floodgate.  When the pressure plate detects water, it will trigger to the 'off' state and send a 'close' command to the floodgate.

[GoldenShadow]

Use the diagonal opening trick. Any water flowing through will be unpressurized. So you can leave your pump running forever, but make the water enter your cistern from a diagonal, and it will never raise above the point of entry, no matter how high the water source is.

[i2amroy]

Just a piece of advice here, and that is that you don't want to use floodgates or bridges for automatic cisterns. This is due to the open/close delay that can really cause some problems. Example:
1)Water is low and triggers pressure plate to open gate
2)While gate is waiting to open, a 1/7 of water moves over and deactivates the pressure plate, sending the close command.
3)This command is then ignored because the gate is still opening.
4)Gate remains open and fort floods with watery death.

This is simplified down of course, but the point is that bridges and floodgates when dealing with a multi /7th's reservoir can get really messed up due to the delay. As such I strongly suggest that you either use a door for all of your reservoir openings, or simply connect it to a lever that you open once every few years to refill.

Also Rather then using 2 pressure plates I'm fairly certain that you can just set a minimum and a maximum for a single plate, so that it is only triggered when the water is between those two values and is "off" when the water is above or below them.

[DVeL]

How about doors? They open and close immediately, so water shifting back and forth over the pressure plate and toggling it constantly won't spam the door with commands it can't carry out until it's done executing the last one.

Depressurising the water at the appropriate level is probably the safest option. Alternatively, you could have a pressure plate on the level above the reservoir set to close the floodgate if it detects any water at all.

And how can i set pressure plate to CLOSE floodgate? My own attempts never succeeded.

Set the pressure plate to trigger when there is no water (level 0-0 or 0-1).  Link it to the floodgate.  Also build a lever and link it to the floodgate.  Pull the lever, this will open the floodgate.  When the pressure plate detects water, it will trigger to the 'off' state and send a 'close' command to the floodgate.

Wow, thank you! It really helped. I thought about the same design myself, with one small difference - I tried to set 0-7 water level, and the floodgate didn`t respond. Now i get the meaning of the second number =)
DF mechanics became a bit more clear.